Google Talk did have XMPP functionality, which allowed for SASL. [1] But of course, they killed this off because they wanted to dominate chat and messaging with their own proprietary protocol.
If they had not followed this strategy they would be killing in this market, even whilst supporting XMPP Federation. But they have chosen to release multiple proprietary products, so they aren't the lead in the market. Silly of them really, and it just shows you they aren't really the nimble company they once were.